The design of 2D (referred as 2D or cylindrical blade having identical cross-section throughout the blade span) and 3D blades are of paramount importance for power generation. Various patents, e.g. U.S. Pat. No. 5,779,443 (1998), U.S. Pat. No. 5,211,703 (1993) and U.S. Pat. No. 5,192,190 (1993) refer to “stationary” blade. U.S. Pat. No. 5,779,443 deals with radially bent blade (radial shift of centers of areas of individual profiles over the blade height). The present invention refers to design of six base profiles and construction of moving blade (by making use of these base profiles) without radial shift for the use in steam turbine for power generation. The Redding patent (U.S. Pat. No. 2,415,847) refers to a set of six profiles for the compressor machine. It is not meant nor can be used for turbine applications.
In cylindrical stages, the profiles remain same for more than one stage over their blade height without significant loss in efficiency. The inlet flow is more or less uniform over the blade height. Usually a few profiles are sufficient to create many blade rows. The present invention primarily concerns to moving blade of axial steam turbines and the turbine stages, where the direction of incoming flow to moving blade varies along the blade height, thus necessitating twisted blade. Hence the design and manufacturing of twisted blade is costly and time consuming as it is to be done every time for varying flow condition.
Normally the conventional blades are of constant cross-section and cylindrical in shape over the blade height. At any cross section the shape of the profile remains same as shown typically in FIG. 1. The profile or section is made of two surfaces, suction face and pressure face, each joining leading edge to trailing edge. X-axis and y-axis coincide to turbine axis and circumferential direction, respectively.
The center of gravity lies at origin of coordinate axes. The blade or profile is set at angle ‘betabi’ or y,tg (or gamatg), also known as stagger angle with respect to U-axis. Chord is defined as axial distance of base profile measure between two farthest tangents to the profile; one at leading edge side and other at trailing edge side. The tangents are normal to the chord. Axial chord is the projected length of the profile on X-axis; hence varies with profile stagger. Inlet and exit flow angles β1,tg and β2,tg are fluid flow angles with respect to tangent (U-axis), respectively. The profile faces can be specified by various ways, e.g. through discrete points (x, y co-ordinates), through a set of arcs and through bezier points.
In this invention new 3D blade can be made of many such profiles (FIG. 1) but with varying shape and other parameters such as stagger angle, chord, axial chord, cross sectional areas (FIG. 2). The centers of gravity of the profiles coincide in x-y planes. The areas of cross section, stagger angles, and the ratio chord (c)/pitch (s) monotonously decrease from hub to tip, whereas pitch (=2Πr/no of blades; r=radius where the profile is located) increases along the blade height. A typical sketch of such set of stacked profiles for all six sections and blade-to-blade (cascade) view are. shown in FIG. 2.